Note 3 - Merger with Nicor (Detail) - Preliminary Rollforward of Total Goodwill Recognized (USD $) In Millions, unless otherwise specified	4 Months Ended
	Mar. 31, 2012		Dec. 31, 2011		Dec. 08, 2011	Mar. 31, 2011
Balance	$ 1,813		$ 1,813		$ 418	$ 418
Merger with Nicor	1,395
Distribution Operations [Member]
Balance	1,586		1,586		404	404
Merger with Nicor	1,182
Retail Operations [Member]
Balance	124		124		0	0
Merger with Nicor	124
Wholesale Services [Member]
Balance	2		2		0	0
Merger with Nicor	2
Midstream Operations [Member]
Balance	16		16		14	14
Merger with Nicor	2
Cargo Shipping [Member]
Balance	77		77		0	0
Merger with Nicor	77
All Other Segments [Member]
Balance	8	[1]	8	[2]	0	0	[1]
Merger with Nicor	$ 8

[1] Our other segment's assets consist primarily of cash and cash equivalents, PP&E and the effect of intercompany eliminations.

[2] Our corporate segment's assets consist primarily of cash and cash equivalents and PP&E and reflect the effect of intercompany eliminations.